Linux commands-help command: Helper

Which CD   find the location of the CD command which umask  find the location of the umask command

The shell is the command interpreter, that is, when you hit a command, who will pass the command to the kernel, the kernel runs to return a result, who shows you this result, who is the shell. Image, it is equivalent to a shell.

In a Linux system, commands that use which to find the path to the command are shell built-in commands, and help is used if you want to get the shell's built-in commands.

Help Umask  can view the helper content of the shell's built-in command umask

Linux commands-help command: Helper